A new study in mice suggests psychedelics make the brain more likely to 'see' images from memory rather than what's actually in front of it. Long before modern laboratory testing, indigenous cultures used these substances to treat psychological and physical ailments. The Aztecs used psilocybin mushrooms as medicine, while Andean cults consumed mescaline-rich San Pedro cacti thousands of years ago. Archaeologists have found a ritual bundle thousands of years old in a Bolivian cave that contains